The management of hazardous waste materials, including radioactive, biological and chemical waste, is of critical concern to maintaining a safe environment. For chemical and biological wastes, the hazardous material initially may be contained in a vessel, and while in the vessel may be processed and rendered benign. Management of radioactive waste materials, however, raises special concerns since certain nuclear waste materials retain high levels of radioactivity for thousands of years. An initial concern in the management of these radioactive waste materials is the safe local containment of the materials as they are generated. Also of concern is the safe transport of the locally contained materials to specialized facilities for processing or for intermediate term or long-term storage. Thus, for example, high-level radioactive waste materials produced at nuclear utility sites are typically contained locally for a period of tens of years. Subsequently, plans call for these waste materials to be transported to a specialized facility for longer term storage and/or waste processing. In such intermediate term storage facilities, radioactive waste materials may be stored in containers for 40 to 100 years, with the containers being available for periodic integrity confirmation and the contents being accessible for retrieval and inspection. Subsequent to the intermediate storage period, the radioactive waste materials may be processed or transported to other specialized sites for long-term storage, for example, of from 300 to 1,000 years. One such long-term storage site is currently planned for the Tuff Repository in Nevada.
Presently, two arrangements for the short-term local storage of radioactive spent fuel rod assemblies predominate. Both arrangements have been designed to dissipate heat from the fuel rod assembles rapidly so as to prevent thermal breakdown of the assemblies as a result of overheating. In one arrangement, the spent nuclear fuel rod assemblies are stored exposed at the generation site in large pools of water. Elaborate systems are required not only to cool the water to a desired temperature, but also to chemically treat the water to provide radiation shielding between adjacent assemblies. In the other technique, the spent nuclear fuel rod assemblies are placed in racks surrounded by stainless steel containers which, in turn, are enclosed in concrete bunkers. Since stainless steel does not provide a sufficiently high thermal conductivity, a constant flow of air is forced through the containers to dissipate heat from the waste materials therein. This flow of air contacts the nuclear fuel rod assemblies directly and is then exhausted into the environment. Both of these arrangements require large storage areas, constant maintenance and rather elaborate systems to maintain the stability of the radioactive waste materials. Furthermore, where stainless steel containers are used, the containers are susceptible to swelling and corrosion, thereby jeopardizing the safety of the storage arrangement over long periods of time.
The growing inventories of spent nuclear fuels has resulted in an increasing urgency to develop containers and overall systems for the safe storage of these materials, both short term and long term. Despite the many efforts that have been made to address these concerns, there still exists a need for a simple, safe and economical system for containing and storing radioactive waste materials for prolonged periods of time. Preferably, such system will enable the waste materials to be accessed periodically for inspection and/or processing.